![Very Happy :D](./images/smilies/icon_biggrin.gif)
So. I work on a LOT of tubeamps. Mainly for guitar/bass use though,so using tubers at home had to this point been redundant. As such the time had come to go that route however.
German e-bay was scavenged for a donor and after some going back and forth and i won an auction for this old Braun CSV-13.
Certainly not in the best of nicks,but at least all original and in one piece.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_4%7E131.jpg)
As i took delivery of the amplifier the first thing i did was to take the lid off,and what greeted me was 50years of dustbunnies,nicotine and plain old junk. 1 liter of rubbing alcohol and a brush followed by liberal use of window cleaner later though the amp looked about like new on the inside.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_5%7E124.jpg)
All the stock tubes from Tfk and Valvo were still in place. In fact,the amp had from the looks of it never been touched on the inside.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_6%7E117.jpg)
So. What i basically had on my hands was this really nice looking unmolested mid -60´s piece that in essence just craved for a little aesthetic attention on the outside really.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_7%7E106.jpg)
Yep. 100% stock. All the way.
As i hooked my multimeter up and started to check things out from a practical point of view however it soon enough became evident that the amp lacked out in the service dept. In short,it needed some fresh components tossed at it in the form av e-lytes (elkos) and what have you not.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_8%7E97.jpg)
The PCB´s (platine) looked about as new too after the thorough clean.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_10%7E79.jpg)
Upon a simple checkup with my DMM it turned out that first of all voltage was WAY down for the rectified front end heaters,i had like just atop 6VDC or so,and in turn there was approx 30VAC worth of ripple in the HT circuit. In short,this had to be handled.
That and....
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_12%7E72.jpg)
...this,had to be handled as well IMO. As i´ve bought this CSV to be a performer more than a conversation piece i had my heart set die hard at replacing the old onboard selenium rectifiers too.
First of all old selenium rectifiers that has been loaded heavily might very well have developed arching issues within,creating an even larger voltage drop than when new,and in turn they ain´t the most reliable thing around. Atop that,WHEN they actually go "boom" selenium is released into free air and that stuff is toxic beyond belief.. So. Replacement with current day and era silicone was in order.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_14%7E76.jpg)
Both rectifiers were replaced with common silicone units,and the elkos in turn were replaced by axials in my case. The latter an easy decision as axials are way cheaper than the "tower" F&T ones up here in Sweden.
At the same time the electrolytes for the bias/heater circuit were replaced as well of course,as was the odd critical high power resistor.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_15%7E66.jpg)
Seing that component size has gone down a bit in 50 years that left this area basically vacant. This then where the stock HT selenium rectifier resided stock.
![Bild](http://102983.org/gallery/albums/userpics/10003/normal_16%7E59.jpg)
So called 1 Ohm "bias resistors" were installed. Although i certainly own bias testers the install of qualified 1 Ohm resistors make this a once done deal. In short,no matter who down the line can easily check bias of each powertube with a common multimeter.
If you look closely at the picture though yet another modification has been pulled,and that is the install of a 25V zener heading for each screen grid.
The point here being that by the swap from selenium to silicone and in turn the implement of fresh elkos B+ voltage jumped. Something that really is all good,however..
The old Valvos i know to be able to take a hell of a beating when asked to,not so however with newer day and era tubes like commonly available JJ´s or whatever.
To have 340VDC riding on the anodes/plates of the powertubes is perfectly safe,however...when pushed B+ will plummet a bit and doing so it might very well produce a situation where the screens will turn positive as far as potential vs the anodes/plates and see...the screens of modern day tubes are simply not designed to handle that.
Something i know of all to well from working on instrument amps,that commonly are run wide open throttle.
So. One way of handling that in an easy manner is the install of them 25V zener diodes. No matter the transients voltage will now regardless always be them 25V lower than B+ voltage.
In practice this also brings a "snappier" powerstage. In short you´ll come to experience the amplifier being "more powerful" (while it´s not) when you start to push it.
This is a trick i use in many an old guitar/bass tube amp when called for and it really works wonders.
Another "feature" that came up as a function of replacing the rectifiers was that now the DC voltage for the front tube heaters was to high.
Easy enough to remedy by simply replacing the stock 26 Ohm highpower resistor in the circuit with two 15 Ohm,for 30 Ohm total,in series. Made front end heater voltage clock in at 12.0VDC sharp.
As is i run the amp in 240VAC mode. Have used it a fair bit here at home hooked to my surround and...i´m happy as pie with it!
![Very Happy :D](./images/smilies/icon_biggrin.gif)
I run it through a pair of Tannoy floor speakers,and the "tube" difference is all there-no argument.
To a degree where i´ve decided to buy yet another one and overhaul to be able to enjoy tube power in the 4 corners of the room.
Further,i plan to compliment them with a Braun PS turntable (plattenspieler) as time passes but am still undecided on which model though.
Remains the aesthetics then. I´ll hold my horses and refrain from handling that until the next unit is done and residing by the first one and then plan to have both the sheet metal "covers" of both amplifiers powder coated light grey-per stock. Sorry to say that´ll make away with the lettering out back,but you can´t win them all i guess
![Sad :(](./images/smilies/icon_sad.gif)
On the other hand..when powder coated there will be two specimen of the old Braun CSV-13 residing here at home..being all they can be.
Btw.
It is my understanding that these amplifiers came in two versions? Circuitry wise that is? I read up over the internet how to convert them into RIAA standards,vs the CCRI that was supposed to be stock. However,upon closer examination of the unit i´ve got it turned out that it already was RIAA in as much that the entry stages gridleaks for the phono part of it already was 47k,and this had not been touched since new.
In short,are my findings on the matter correct?
That these amps came in EITHER RIAA or CCRI standard?
Cheers!
/Jesper